The present invention relates to a method for the sterilization by substituting the dissolved oxygen in milk or the like (defined hereinafter) with nitrogen gas in a sterilization of milk or the like, to a product prepared thereby and to an apparatus for substituting with nitrogen gas.
With regard to a method for removing the dissolved oxygen in liquid, a physical method such as an injection method and a tower flushing method and a chemical method using a deoxidizer have been known.
In substituting the dissolved oxygen in liquid with gas, a method where the gas which is used for the substitution is directly injected into a tank of the liquid using a pipe or the like followed by mixing to substitute with the gas has been known.
A gas mixing apparatus in which nitrogen gas and milk or the like are placed in a mixer and stirred whereby oxygen gas is substituted therewith has been known (Japanese Patent No. 2,805,593).
A method in which the oxygen in milk, unheated solution containing milk, fruit juice, etc. is substituted with gas and the dissolved oxygen amount in the liquid is reduced to carry out the sterilization has been known as well (Japanese Patent Laid-Open Publication No. Hei-10(1998)/295341, i.e., JP-A 10-295341).
In the present invention, the matters to be solved are that, when a sterilization is carried out at high temperature (such as at 130xc2x0 C. for 2 seconds) for making the long preservation of milk or the like possible, sulfides which are the causing substances or the so-called heated smell are generated whereby taste and smell of the beverage is deteriorated.
Most of the said sulfides are dimethyl sulfide and dimethyl disulfide and, since they greatly deteriorate the taste and the smell of the heat-sterilized product, it has been demanded to suppress the generation of the sulfides in carrying out the sterilization.
As such, in order to manufacture a product which can be preserved for long period, the sterilizing condition has been necessary to be at 130xc2x0 C. for 2 seconds and there is a problem that, when sterilization is carried out under such a condition, generation of the sulfides is inherently unavoidable.
Under such circumstances, there has been a demand that, even when sterilization is carried out under such a high temperature condition necessary for preservation for a long period, production of sulfides is suppressed to such a low extent that the taste and the smell are not deteriorated.
With regard to a means for solving that, a sterilization under the reduction of the dissolved oxygen in the liquid which is to be sterilized is effective and, as one of the methods for reducing the dissolved oxygen in the liquid, substitution of the dissolved oxygen in liquid with an inert. nitrogen gas has been carried out.
As to a method for substituting with nitrogen gas as such, physical and chemical methods have been proposed already but, in the sterilization of milk or the like, all of those methods have a low substituting efficiency and, especially in the case of a mechanical mixing and dispersing of the gas, a great volume of foam is generated whereby there is a problem that, in order to improve the efficiency, the equipment becomes large in size and the cost becomes high.
An object of the present invention is to provide a practical method and apparatus of a low cost and without a large device whereby the above-mentioned problem is solved.